1. Field of the Invention
The present invention is directed to linear rotary bearings. More particularly, the present invention is directed to linear rotary bearings wherein load bearing elements circulate freely to support large loads relative to the size of the bearing.
2. Brief Description of the Prior Art
Bearings which permit both linear and rotary movement of a machine part on a shaft have been known for a long time. Examples of varying constructions of such linear rotary bearings can be found in U.S. Pat. Nos. 4,025,128; 4,303,280; 3,086,824; 3,751,121; 3,446,540, 3,037,821; 3,582,160, and 3,692,371. Ball elements which move in dedicated guide channels in closed loop paths as the bearing moves linearly relative to its supporting shaft, comprise a common feature of the above-noted prior art linear rotary bearings.
As is well appreciated by those skilled in the art, machining the relatively complex loops and guide channels of the above-noted prior art linear rotary bearings is rather labor intensive. Therefore, these prior art bearings are rather expensive. In addition, the dedicated ball channels of some of the prior art bearings cause the supporting shaft to wear unduly fast at certain locations.
In order to avoid the above-noted undue wear of the shaft in fixed locations where the balls repeatedly contact the shaft, the prior art provided relatively complex ball guide channel configurations which have a tendency to distribute the load more evenly over the shaft. The linear rotary bearings described in U.S. Pat. No. 3,086,824 are particularly noteworthy in this regard, because these bearings incorporate cross-over passages between the several guide channels so that the balls circulate in a predetermined pattern in the assembled bearing. Examples of ball spline assemblies which have similar circulating ball channels for linear movement of the spline, relative to a shaft, are found in U.S. Pat. Nos. 2,945,366, 4,309,061, and 4,127,309.
The linear rotary bearings of the prior art are, however, still less than satisfactory from the veiwpoint of complexity of construction and therefore cost. Moreover, the relatively complex ball circulating structures and channels built into the prior art linear rotary bearings cause the bearings to have only small load bearing capacity relative to their size. The present invention solves the above-noted problems, and provides linear rotary bearings of relatively simple construction which nevertheless have relatively high load bearing capacity.